Oxygen metabolism is assisted by metalloproteins containing copper and iron at their active sites. Oxygen transport for respiration is carried out by the iron proteins, hemoglobin and hemerythrin, or the copper protein, hemocyanin. Catabolism of organic compounds by oxidative pathways is catalyzed by both iron and copper enzymes which interact simultaneously with a substrate and molecular oxygen. In our resonance Raman spectroscopic studies of hemerythrin and hemocyanin, we obtained new molecular and electronic structural information on the functional role of the metal ions and the mode of oxygen bonding to these proteins. We intend to pursue further investigations on these respiratory proteins and to initiate research on several oxidases, oxygenases and redox proteins. We wish to gain a better understanding of the physiological functions of the metal ion sites as acquired from an elucidation of their molecular enviornments and the changes in the electronic structures of the metal-ligand complexes during their reactions. We shall continue to provide detailed assignments of the optical spectra of the metalloprotein chromophores from studies of their resonance Raman intensity enhancement profiles. The novel technique of resonance Raman spectroscopy permits direct observations of vibrational modes of the active sites of metalloproteins since it results from the interaction of their vibrational and electronic energy states. It is, therefore, a specific and selective probe of the chemical structure of the chromophore. This technique is generally non-destructive and applicable to samples at physiological concentration in aqueous environments. Our investigations on the structure-function relationships of metalloproteins will be augmented by synthesis and structural characterization of iron and copper complexes which serve as model compounds for the active sites of metalloproteins.